RESEARCH PAPER NUMBER THIRTY-FIVE
JUL 12 1942
APPLICATION OF THE
PRINCIPLE OF DISPERSION
TO PORTLAND CEMENT
EDW. W. SCRIPTURE, JR. t PH.D.
Master Builders Rehe>trch Laboratories
COPYRIGHT 1941 - THE MASTER BUILDERS COMPANY
EXfilXEERS, architects and those connected with
the various phases of construction are well ac-
quainted with the many improvements made in the
manufacture of Portland cement since its introduction.
They are familiar with the facts that better design of
mixes and more care in the selection of aggregates have
vastly increased the quality of concrete and mortar.
but i hey are also aware that an important problem
o do with durability and the other prop* -
of concrete remained to be solved: the redaction of
watei necessary to place all concrete. Leading
investigators have seen the vital need for this improve-
ment while observing the performance of concrete
during and after placement in many existing structures,
and also in the upkeep costs of structural repairs
of railroads, utilities and other large industrial
The Researcn i^aDoraiory of The Master Builders
Company recently announced a new principle for the
improvement of concrete and mortar — Cement Dis-
persion. They have spent ten years in proving that
by adding to the concrete or mortar mix a < <
dispersing agent the basic problem of all cement mixes
is attacked, namely, tin excess water required for
placeability. Reduction of this water insures improve-
ment of the properties of the structure with respect
to durability, watertightness, strength and other im-
The Master Builders Company feeling 'that the
introduction of this discovery and its application to
practical construction will be welcomed by everyone
connected with the building industry has published
this paper. The following pages set forth the manner
in which dispersing agents function in colloidal systems
generally, and describe the way in which this principle
has been applied to cement for the improvement of
concrete and mortar.
APPLICATION OF THE
PRINCIPLE OF DISPERSION
TO PORTLAND CEMENT
rjORTLAND Cement is an extremely versatile material admirably
\ adapted to a great variety of applications. Its ability to be
placed, mixed with aggregate, in the form of a plastic mass into
anv desired shape and subsequently to harden in that shape make it
a means for carrying out operations of construction which could not
r^adilv be accomplished in any other way. Its low cost makes feasible
structures which could not otherwise be attempted.
In its very strength lies its greatest weakness. To make a plastic
mass from portland cement and aggregate, either mortar or concrete.
it is necessarv to add water. Part of this water is required to combine
with the cement but the greater part of it serves no other purpose than
to make the mix placeable as has been stated by Mr. P. H. Bates: —
"Since the amount of water required to produce the hydration
accompanying maximum development of strength is much less than
that used 'in dry mixes of concrete somewhat less than 18 pounds of
water per bag of cement are needed to produce a decidedly 'complete
hydration": this is less than half the amount used in a 4.5 gallons per
bae mix, usually considered a very dry mix , it can be realized that a
very large part* of the mixing water should really be called 'placing
water, and is needed to get the concrete to where it is desired that it
should harden. We are, therefore, attaining a strength less than the
potential strength and in so doing also materially affecting adversely
the properties of volume change and durability."
Manv attempts have been made to overcome the inherent dis-
advantages from which portland cement suffers. These have taken
various forms. Chemical reagents, such as calcium chloride, have been
added to change the rate of the hydration reaction. Modifications have
been made in the composition of the cement itself. In general such
measures have produced certain results with respect to acceleration,
retardation or similar properties but they have not had any significant
effect in solving the basic problem of eliminating or reducing the excess
water. In order to overcome the tendency, directly attributable to
excess water, of the concrete to absorb water, waterproofing ingredients
of the water-repellant or stearate type have been introduced. These
have served a useful purpose under some conditions, particularly where
no hydrostatic pressure was involved, but have not attacked the
l Trends in the Production and Use of Various Types of Hydraulic Cements by
P. H. Bates, J. Am. Con. Inst., Jan.-Feb. 1935.
fundamental problem. Pozzuolanic materials have been employed to
improve corrosion resistance but these have had to compete with the
increase in water necessitated by their addition to the mix. Other
finely divided powders have been incorporated in concrete mixes for
reasons which were not always clear but usually with the idea that
workability would be improved. Such materials defeat their own
purpose because, far from reducing the amount of water required for
a given consistency they have had precisely the opposite effect. This
situation has been summarized by Mr. F. R. McMillan: — 2
"It can be stated as a general rule that an increase in the necessary
water content of the cementing paste in concrete is detrimental. It
follows, therefore, that any beneficial effect which an admixture may
have must compete with the detrimental effect of any increase in the
water content which its use may incur. This holds for portland cement
as well as for other powdered materials. For example, to add
cement only to the mix will increase the strength to a greater degree
than to add the same amount of cement together with water. The fact
that the addition of cement plus water may show an increase in strength
merely illustrates that the detrimental effect of the added water did
not offset the beneficial effect of the added cement/'
The many expedients which have been tried, whether production
of special cements by altering the composition of the cement itself or
additions to the cement or the mix, have produced, in many cases at
least, desirable results in some particular direction. They have not,
however, been effective in attacking the underlying cause of most of
the weakness of concrete or mortar; the excess water required to make
the mix placeable. It would appear that any radical improvement in
the properties of concrete or mortar should be sought in the reduction
of this 'placing' water. Actually much of the investigational work on
concrete has been direct to this end through mix design, selection of
materials, methods of handling and similar means. As pointed out by
Mr. McMillan 3 the benefits to be derived by these expedients are small : —
"At best, only a bare 5 per cent of the concrete volume in plastic
mixtures can be changed from water into solid material by improve-
ments in grading over what is ordinarily accomplished. This leaves
from 8 to 12 per cent of water, as shown in the figures. It is toward
the reduction of this quantity of water that any proposed improvements
must be directed."
Accepting cements as they are now produced and assuming that
every available advantage has been taken of the best methods of mix
design and concrete handling, there still remains a wide gap between
the properties of the concrete produced and the potential optimum.
The most promising approach to a means of closing this gap lies in a
study of the water-cement paste as a colloidal system and the applica-
tion to it of physico-chemical principles, particularly that of dispersion.
2 A Method of Evaluating Admixtures by F. R. McMillan and T. C. Powers
J. Am. Con. Inst., April, 1934.
3 Basic Principles of Concrete Making — By F. R. McMillan, Pg. 65.
DISPERSION IN A LIQUID MEDIUM
When incorporated in an aqueous medium the particles of a solid
tend to agglomerate and act as large clumps rather than as individual
particles Fig. 1 . This is known as a flocculated condition and is due
to the absence of electrostatic charges on the particles so that when
they collide they tend to stick together. If a dispersing agent is incor-
porated in the "flocculated solid-liquid system then the agglomerates
or clumps tend to be broken up and the solid particles are distributed
more or less evenly through the aqueous medium in the form of
individual or discrete particles. The system is then said to be defloccu-
lated or dispersed (Fig. II . The action of the dispersing agent is
caused by its orientation with respect to the solid particles whereby
these are" endowed with electrostatic charges of like sign so that when
they collide they are mutually repelled and do not tend to stick together.
This effect may also be enhanced by the action of the dispersing
agent as a protective colloid which prevents the particles coming in
close contact with one another.
°00 00 ° O
o o ° o o o °
o o o o
c ° _ o o o
a ° o
° o o o ° °
Dispersing agents are specific in their nature, that is, a dispersing
agent for one solid-liquid system may or may not be a dispersing agent
for some other liquid-solid system. What reagent or reagents will act
as dispersing agent for one particular system depends on the absorption
relations between the dispersing agent and the system and will be
determined by experiment. Dispersing agents, moreover, should not
be confused with wetting agents, emulsifying agents and other surface
active compounds*. Wetting agents are compounds which reduce the
surface tension of water and thereby reduce the interfacial tension
between the water and the solid which is to be wet. Emulsifying agents
are compounds which concentrate at the interface between the con-
tinuous and the emulsified or dispersed phase due to the solubility
relations of the two parts of the molecule. While these reagents may
appear to have some of the characteristics of dispersing agents they
are not dispersing agents and do not produce the same results. Further-
more, these wetting and emulsifying agents tend to cause foaming and
may introduce other extraneous effects in any particular system.
•Fig. Ill— (See pag
~4— In tube containing the
foaming agent, note form-
ation of a stable foam,
which is absent in tube
containing the dispersing
agent. — >-
In this manner the foaming
agent introduces a large
quantity of air into the mix.
DISPERSION OF PORTLAND CEMENT
The operation of dispersing agents has been known and utilized for
a long time with respect to some applications as for example, in the
ceramic industries for the deflocculation of clay slips. Until recently
no dispersing agents have been known which were applicable to the
deflocculation of portland cement. Recent researches have shown that
certain complex organic compounds will disperse cement and will not
have injurious effects such as a marked lowering of surface tension caus-
ing foaming or interference with the hydration reactions of the cement.
The action of a cement dispersing agent on portland cement in
water is similar in its effects to the action of any dispersing agent in
a solid-liquid system. Fig. IV shows photomicrographs (a) of cement
in water in its normal or flocculated condition and (b) of cement in
the dispersed condition, produced by adding a small amount of dis-
persing agent to the water.
The dispersion or deflocculation of portland cement in a concrete
or mortar mix is important in a number of aspects. In general it may
be pointed out that the reactions on which portland cement depends
for its valuable properties are surface reactions. They are, therefore,
a function of the surface area of the cement. For this reason cement
manufacturers have consistently increased the fineness of grinding of
cement clinker. Unfortunately the full surface area produced by fine
grinding is not available for reaction due to the flocculated condition
of the cement in the mix. It is perhaps even more unfortunate that
this agglomerating tendency is even greater with greater fineness so
that the beneficial effects of fine grinding have been in some measure
offset by the formation of clumps. The addition of a dispersing agent
to portland cement mixes has made available for reaction for the first
time the full surface area of the cement particles. A dispersing agent
in a cement mix, therefore, permits utilization of the cement to the
A special Held is that of colored concrete or mortar mixes. To pro-
duce color in a concrete structure suitable pigments are incorporated
in the mix with the cement and in some cases colored aggregates are
used. In such an application a cement dispersing agent offers not only
advantages in relation to the properties of the co \r mortar but
it also effects improvements with respect to the pigment itself. The
ence of the dispersing agent facilitates the dissemination of the
pigmenl uniformly throughout the mix, increases the brilliance of the
resulting color, ; equal color with less pign ei • poration
of any fines including pigments has an adverse effect on the properties
of the mortar since the water requirement of the mix is in<
and overcomes rh«- deleterious effects of man'
**~ Color without dispersing
l settles rapidly in
Dispersed color remains
ipended — ►
EFFECTS OF DISPERSION ON THE PROPERTIES OF
CONCRETE AND MORTAR
Since the properties of concrete and mortar are primarily dependent
on the amount and quality of the cement paste any influence which
alters the nature of this paste will inevitably influence the properties
of the mix Dispersion of the cement basically changes the relations
of the solid particles to the liquid in this colloidal system and conse-
quently may be expected to have a profound influence on many if not
all of the characteristics of the concrete or mortar. These effects may
be divided into two groups corresponding to the two states in which
concrete exists: the transitory plastic stage during placing and the
ultimate hardened mass.
^—Effects of Dispersion During Plastic Stage
The plastic state is vitally important because this is the period
during which the concrete or mortar is placed to fill the space which
it is to occupy, compacted, and finished. Unless the mix is workable
at this time, a sound structure will not be produced regardless of any
other properties of the mix. This property of workability may be
considered as made up of two components: mobility or ease of flow and
cohesiveness or resistance to segregation.
Dispersion of the cement particles will increase mobility or ease of
flow. This is because the water held in the clumps or agglomerates ot
the flocculated cement is released to become a part of the fluid medium
through which the particles move. Further by breaking up these
6 ' _- gals.
1 in .__
Slump 5 in.
clumps the size of the units in the liquid is reduced so that thev can
move more easily past each other in the fluid. The result is a 'more
workable concrete which is more easily handled, or placed with less
danger of the defects commonly due to lack of workability. What is
perhaps even more important is that this permits a more workable mix
to be produced with less water, that is, at a lower water cement ratio.
Cohesiveness is attributable to the attractive forces between sur-
faces. 1 herefore. dispersion of the cement which makes available a
greater surface area will increase the cohesiveness of the mix*. \ first
result is that the mix becomes more "fatty" or "buttery" which is
extremely important in some types of work. An even more generally
important effect is a reduction of the tendency of the components of
the mix to separate, that is, toward segregation. The aggregate is less
apt to separate from the cement paste so that the danger of honey-
combing, sand streaking and similar defects is minimized. In its
upward movement through the mix the water tends to collect under
the larger pieces of aggregate forming pockets on the underside such
that the aggregate is not bonded to the cement paste. The pockets
constitute points of weakness and of attack by destructive agencies.
Separation of the water and fines in an upward direction from the
coarser part of the mix is prevented. By this means 'bleeding' or
watergain and the formation of laitance are eliminated or reduced.
1 he uniformity of the mix in place is enhanced. (Fig. VII— see page 12).
A further effect of dispersion, also due to the greater surface area
available, is a greater force holding the water to the cement particles.
1 his produces higher "water retentivity" which is particularly impor-
tant in masonry mortars where porous masonry units tend to suck water
out of the mortar. It is also important in other mortars and concrete as
it retains the water in the mass promoting better curing.
One phenomenon which occurs in concrete and mortar during the
plastic stage has been rather neglected. This is the volume change or
more specifically shrinkage which occurs before hardening. The volume
changes which occur at this time are in all probability more important
0) This does not contradict the previously made statement
that the dispersion of the cement particles is due to the
repellent action of like electrostatic charges. This repul-
sion which effects dispersion refers to the forces between
the cement particles. The attraction which operates in
connection with cohesiveness refers to the forces between
the cement particles and the other components of the mix,
particularly the aqueous medium in which the cement
particles are dispersed. Since the water does not carry
an electrostatic charge there is no repulsion between it
and the cement particles: hence the attractive forces
between the water and the solids in the mix are dependent
on surface area of the solids.
<— In the flocculated con-
dition the solid particles
settle to the bottom leaving
clear uater at the top;
a condition analogous to
The dispersed particles
remain suspended. — ►"
Untreated i Flocculated
than those which take place subsequently 2 . They are caused by move-
ment of water from one part of the mix to another and by loss of water
from the mix by suction, by evaporation or by other means. Such
volume changes produce incipient or actual cracks which impair the
integrity of the structure and make it susceptible to subsequent attack.
( Fig. VIII). Dispersion of the cement counteracts these volume changes,
first by reducing the amount of water required for a workable mix and
second by imparting higher water retentivity thus resisting movement
and loss of water.
show how cracks
due to shrinkage
open wider and
new cracks appear
CRACKS IN UNSTRESSED CONDITION
CRACKS WHEN LOAD IS APPLIED
( 2 ) "The occurrence of cracks during the 'pre-set' period is so
frequent, especially in flat work, it is surprising suclvlittle
mention has been made of it in concrete literature. Yet
positive, or even incipient, cracks produced in this pre-set
period are often more dangerous to continuity than those
produced by the normal drying out after the cement has
become hard set.
When screeding of flat work or rodding and vibration
of concrete in forms is completed, all solid particles settle
slowly at a uniform rate until the coarser particles become
arched and fixed in the mass. Each smaller size will then
stratify until it in turn touches other particles. This
settling action exposes water at the surface which proceeds
to evaporate in the presence of dry air, warm weather, and
wind, singly or combined. The structure formed by the
settlement of the solids to a rigid condition is rather loose
and the smaller particles are still far from consolidated,
being held apart by the water films on their surfaces.
As the mixture dries out, the contained water moves
through the mass to the drying surfaces and may cause
further readjustments. When drying has proceeded
beyond the point of particle adjustment, air is drawn
into the mass to replace the volumes in the voids formerly
filled with water. From this stage on to the final drying
or to some point before hard set, surface tension plays
its part in the shrinkage of the mass."
C. A. G. Weymouth— J. Am. Con. Inst., Sept., 1940, Supplement Section 1.
The effects of dispersion of the cement particles on plastic concrete
or mortar may be summarized as follows:—
1. More placeable concrete with less water.
2. Increased fattiness.
3. Reduced segregation and bleeding.
4. Greater water retentivity.
5. Reduced shrinkage before hardening.
B .— Effects of Dispersion on Hardened Concrete or Mortar
Dispersion affects practically all the important properties of the
hardened concrete or mortar. This is due primarily to two causes.
First, the reduction of the amount of water required in the mix pro-
duces the well-known beneficial effects of reduced water-cement ratio
and reduced water per unit volume. (Fig. IX). Second, the dispersion
of the cement particles produces a finer grained structure in the cement
paste and an increased surface area such that the hydration reactions
of the cement will proceed more effectively and more efficiently. Some
of the more important properties may be considered in somewhat
4' 2 gals.
Durability — Durability means the ability of the structure to
resist destructive agencies. These are commonly corrosive solutions
and freezing and thawing. Since the attack of corrosive solutions is
a reaction occurring at the surface where the solution comes in contact
with the cement the rapidity of attack is dependent primarily on the
ability of the corrosive solution to penetrate into the structure, second-
arily, on the ability of the cement itself to resist attack. The ability of
the solution to penetrate is governed by the same factors which con-
tribute to watertightness. Hence, a dispersing agent increases resistance
to corrosion. (Fig. X).
Corrosion tests on 1 :3 standard sand
mortars, cured 7 days. Cylinders show
result o£ 6 months 1 immersion in 8%
Disintegration by freezing and thawing is also primarily dependent
on the ability of water to penetrate into the concrete where it will
freeze, expand and break down the structure, secondarily, on the
strength of the cement paste to resist this force. Since a dispersing
agent reduces permeability and in other ways makes the concrete more
water-tight and since it also increases strength, it will markedly increase
resistance to freezing and thawing. (Fig. XI.;
Untreated Concrete - 150 Cycles of Freezing and Thawing,
Loss in Weight -
te, Same Design and Consist]
\i> Thawing - Lose m weioh-i - 101
WaL 8 Watertightnese is dependent on freedom from
-edom from cracks and on permeability. Since the
A a disp< - ent, as previously discussed, results in an impi
ment in all these respects it will increase watertight!.'
ngth will be incn
h ipenuon I
lead i to
menl in tren •' I
proportional to I he
The reduction ii
by the u i
Volume Change — Volume change or shrinkage is proportional
to the volume of cement paste per unit volume of concrete, that is,
the volume of cement plus the volume of water. Reduction in the
water then reduces volume change.
Uniformity -The uniformity of the hardened structure and
freedom from gross defects will be improved due to the improvement
in the properties of the plastic mix as described previously.
The effects of a dispersing agent on the properties of the hardened
concrete or mortar may be summarized as follows: -
1. Increased durability and longer life.
2. Increased watertightness.
3. Higher strength.
4. Lower volume change.
5. Lower permeability or absorption.
6. Greater uniformity and freedom from gross defects.
The basic reason that concrete and mortar do not realize the full
potential qualities which are warranted by the inherent characteristics
of portland cement lies chiefly in the excess water required for place-
ability. Any improvements to be expected in the properties of concrete
will naturally follow from methods which permit this excess water
to be reduced. An attack on this problem has been made from the
point of view of a study of the physico-chemical characteristics of the
cement-water paste. The result of this work has been the application
of the principle of dispersion to the system.
A cement dispersing agent radically alters the physical nature of
the paste in such a manner that placeability can be attained in concrete
and mortar with a substantial reduction in the water required. This
in turn has profound effects with respect to improvement of durability,
watertightness, strength, volume change and other properties.
It will be realized that this principle of cement dispersion is applic-
able to concrete and mortar generally. Since the many applications of
cement mixes require some variations in the properties of the different
mixes, some modifications of or additions to the cement dispersing
agent may be desirable, but the principle of reduction in water by
means of dispersion will remain universally beneficial wherever
cement is used.
Master Builders Research Laboratories
CEMENT DISPERSION PRINCIPLE
The principle of dispersion of cement is applicable to any type of
work involving cement in mortar or concrete. This work is of a very
varied nature and for different applications somewhat different proper-
ties are required. To accomplish this purpose the cement dispersing
agent may be combined with other basic principles for the improvement
of specific properties of concrete and mortar, as illustrated by the
diagram below. These include pozzuolanic activity, stearate water-
proofing, chemical hardening, and metallic aggregates.
The Master Builders Company has developed a group of products
adapted to various specific concrete and mortar applications. The
exclusive dispersing agent is incorporated in each of these products
in a manner to impart the maximum effect on the resultant structure.
These products are as follows:
( oncrete (General)
High Early Strength Concrete
Concrete (Exposed to Capillary
Moors — Heavy Duty
Floors - Light Duty
i olored Floors
Colored Brick Mortar
tuting and Maintenance
High Early Pozzolith
Omicron Waterproofing and Stearox
Colored Metalicron and Colormix
Omicron Mortarproofing ("O. M/')
Colored Omicron Mortarproofing
Emheco and Metallic Waterproofing
PRODUCT COMPOSITION DIAGRAM
THE MASTER BUILDERS COMPANY
Factories in Cleveland
All Principal Citie*